@ConfigurationProperties源码分析一

野性酷女 2022-03-07 11:20 335阅读 0赞

# @ConfigurationProperties源码分析 一 #

[@ConfigurationProperties源码分析 二 什么时候注册的ConfigurationPropertiesBindingPostProcessor？][ConfigurationProperties_ _ _ConfigurationPropertiesBindingPostProcessor]  
[@ConfigurationProperties源码分析 三 什么时候注册的ConfigurationClassPostProcessor？][ConfigurationProperties_ _ _ConfigurationClassPostProcessor]  
[@ConfigurationProperties源码分析 四 什么时候注册的ConfigurationPropertiesBindingPostProcessorRegistrar？][ConfigurationProperties_ _ _ConfigurationPropertiesBindingPostProcessorRegistrar]  
[@ConfigurationProperties源码分析 五 如何实现递归赋值配置类成员变量？][ConfigurationProperties_ _]

## 背景 ##

之前我们项目当中，配置文件是通过 ***@Value("$\{zk.register.merinfo\}")*** 方式注入的。  
造成问题如下：

*  配置属性不统一，没有结构。
 *  注入麻烦每个属性都要写配置名，和属性名。（只要有重复的工作，就应该重构）
 *  配置零散在项目中各处

@Component
    public class ApiBaseInfoService {
    
    	@Value("${zk.register.merinfo}")
    	public String merInfoRpc;
    	
    	@Value("${pay.qpass.trade}")
    	public String payQpassTrade;
    	@Value("${pay.qpass.refund}")
    	public String payQpassRefund;
    	@Value("${pay.qpass.reverse}")
    	public String payQpassReverse;
    	
    }

修改后我们的代码如下.

@Configuration
    @ConfigurationProperties(prefix = "jlpay")
    @Data
    public class TestConf {
        private  Notify notify = new Notify();
        private  String node;
    
        public static TestConf TestConfStatic ;
        {
            TestConfStatic =this;
        }
        @Data
        public   class   Notify {
            String risk;
            String  trans;
        }
    }

jlpay:
      notify:
        risk: risk-url
        trans: trans-url
      node: node-url

## 问题 ##

那么就是是如何通过@ConfigurationProperties 将配置文件中的值赋值到配置类里面的呢？  
猜想如下：

**既然有注解，那肯定有注解处理器。  
在配置类初始化的时候调用注解处理器处理  
注解处理器会读取@ConfigurationProperties 注解的对象  
获取配置文件中的prefix，和注解对象的类成员变量  
递归将配置属性赋值给类成员变量**

## 源码分析 ##

#### ConfigurationPropertiesBindingPostProcessor ####

Spring 初始化Bean 的时候会调用 bean后置处理 ConfigurationPropertiesBindingPostProcessor 的postProcessBeforeInitialization方法  
这里其实就是我们上面猜想的注解处理器，它会处理ConfigurationProperties注解  
获取配置文件中的prefix，和注解对象的类成员变量

@Override
    	public Object postProcessBeforeInitialization(Object bean, String beanName)
    		throws BeansException {
    			//获取@ConfigurationProperties注解信息
    			ConfigurationProperties annotation = getAnnotation(bean, beanName,
    			ConfigurationProperties.class);
    			//有注解的才绑定配置属性 没有的直接返回
    			if (annotation != null) {
    				bind(bean, beanName, annotation);
    			}
    			return bean;
    	}

private void bind(Object bean, String beanName, ConfigurationProperties annotation) {
    		ResolvableType type = getBeanType(bean, beanName);
    		Validated validated = getAnnotation(bean, beanName, Validated.class);
    		Annotation[] annotations = (validated != null)
    				? new Annotation[] { annotation, validated }
    				: new Annotation[] { annotation };
    				//将bean 类型 注解等信息包装传递给后面处理
    		Bindable<?> target = Bindable.of(type).withExistingValue(bean)
    				.withAnnotations(annotations);
    		try {
    		//委托配置绑定器来处理
    			this.configurationPropertiesBinder.bind(target);
    		}
    		catch (Exception ex) {
    			throw new ConfigurationPropertiesBindException(beanName, bean, annotation,
    					ex);
    		}
    	}

#### ConfigurationPropertiesBinder ####

上面的注解处理器委托配置绑定器ConfigurationPropertiesBinder来处理 ，主要考虑职责分离。

public void bind(Bindable<?> target) {
    		ConfigurationProperties annotation = target
    				.getAnnotation(ConfigurationProperties.class);
    		Assert.state(annotation != null,
    				() -> "Missing @ConfigurationProperties on " + target);
    		List<Validator> validators = getValidators(target);
    		BindHandler bindHandler = getBindHandler(annotation, validators);
    		//委托Binder处理
    		getBinder().bind(annotation.prefix(), target, bindHandler);
    	}

#### Binder ####

委托Binder处理

private Binder getBinder() {
    		if (this.binder == null) {
    			this.binder = new Binder(getConfigurationPropertySources(),
    			getPropertySourcesPlaceholdersResolver(), getConversionService(),
    			getPropertyEditorInitializer());
    		}
    		return this.binder;
    	}

private Object bindBean(ConfigurationPropertyName name, Bindable<?> target,
    			BindHandler handler, Context context, boolean allowRecursiveBinding) {
    		if (containsNoDescendantOf(context.streamSources(), name)
    				|| isUnbindableBean(name, target, context)) {
    			return null;
    		}
    		//用于递归绑定bean属性的绑定器。 理解成回调函数，后面会递归调用给bean属性赋值
    		BeanPropertyBinder propertyBinder = (propertyName, propertyTarget) -> bind(
    				name.append(propertyName), propertyTarget, handler, context, false);
    		Class<?> type = target.getType().resolve(Object.class);
    		if (!allowRecursiveBinding && context.hasBoundBean(type)) {
    			return null;
    		}
    		//用了java8 lambda 表达式 和流操作
    		return context.withBean(type, () -> {
    			Stream<?> boundBeans = BEAN_BINDERS.stream()  // BEAN_BINDERS对象 实际是 JavaBeanBinder List
    					.map((b) -> b.bind(name, target, context, propertyBinder));
    			return boundBeans.filter(Objects::nonNull).findFirst().orElse(null);
    		});
    	}

#### JavaBeanBinder ####

上面的BEAN\_BINDERS对象 实际是 JavaBeanBinder List

private static final List<BeanBinder> BEAN_BINDERS;
    	static {
    		List<BeanBinder> binders = new ArrayList<>();
    		binders.add(new JavaBeanBinder());
    		BEAN_BINDERS = Collections.unmodifiableList(binders);
    	}

遍历属性赋值

private <T> boolean bind(BeanPropertyBinder propertyBinder, Bean<T> bean,
    			BeanSupplier<T> beanSupplier) {
    		boolean bound = false;
    		for (Map.Entry<String, BeanProperty> entry : bean.getProperties().entrySet()) {
    			bound |= bind(beanSupplier, propertyBinder, entry.getValue());
    		}
    		return bound;
    	}

递归调用

private <T> boolean bind(BeanSupplier<T> beanSupplier,
    			BeanPropertyBinder propertyBinder, BeanProperty property) {
    		String propertyName = property.getName();
    		ResolvableType type = property.getType();
    		Supplier<Object> value = property.getValue(beanSupplier);
    		Annotation[] annotations = property.getAnnotations();
    		//这里就是上面提到的回调函数，会递归对象属性赋值
    		Object bound = propertyBinder.bindProperty(propertyName,
    				Bindable.of(type).withSuppliedValue(value).withAnnotations(annotations));
    		if (bound == null) {
    			return false;
    		}
    		//判断有setter方法，调用赋值，用的是java 反射技术
    		if (property.isSettable()) {
    			property.setValue(beanSupplier, bound);
    		}
    		else if (value == null || !bound.equals(value.get())) {
    			throw new IllegalStateException(
    					"No setter found for property: " + property.getName());
    		}
    		return true;
    	}

**主要就是这里实现赋值的 property.setValue(beanSupplier, bound);用的是java 反射技术**

public void setValue(Supplier<?> instance, Object value) {
    			try {
    				this.setter.setAccessible(true);
    				this.setter.invoke(instance.get(), value);
    			}
    			catch (Exception ex) {
    				throw new IllegalStateException(
    						"Unable to set value for property " + this.name, ex);
    			}
    		}

# 总结 #

究竟是如何通过@ConfigurationProperties 将配置文件中的值赋值到配置类里面的呢？

**注册了ConfigurationProperties 注解处理器ConfigurationPropertiesBindingPostProcessor，它实现了Spring容器的postProcessBeforeInitialization方法，会在bean初始化之前被调用  
注解处理器会读取@ConfigurationProperties 注解的对象  
获取配置文件中的prefix，和注解对象的类成员变量  
然后递归将配置属性赋值给类成员变量**

# 链接 #

其他问题

*  [什么时候注册的ConfigurationPropertiesBindingPostProcessor？][ConfigurationProperties_ _ _ConfigurationPropertiesBindingPostProcessor]  
    [\- 如何实现递归赋值配置类成员变量？][ConfigurationProperties_ _]

## github ##

[完整代码][Link 1]

[ConfigurationProperties_ _ _ConfigurationPropertiesBindingPostProcessor]: https://blog.csdn.net/qq_15288023/article/details/88607163
[ConfigurationProperties_ _ _ConfigurationClassPostProcessor]: https://blog.csdn.net/qq_15288023/article/details/88635168
[ConfigurationProperties_ _ _ConfigurationPropertiesBindingPostProcessorRegistrar]: https://blog.csdn.net/qq_15288023/article/details/88634483
[ConfigurationProperties_ _]: https://blog.csdn.net/qq_15288023/article/details/88637675
[Link 1]: https://github.com/396191970/learn/tree/master/demo-configuration